1、BRITISH STANDARD BS EN 12502-4:2004 Protection of metallic materials against corrosion Guidance on the assessment of corrosion likelihood in water distribution and storage systems Part 4: Influencing factors for stainless steels The European Standard EN 12502-4:2004 has the status of a British Stand
2、ard ICS 23.040.99; 77.060; 91.140.60 BS EN 12502-4:2004 This British Standard was published under the authority of the Standards Policy and Strategy Committee on 19 January 2005 BSI 19 January 2005 ISBN 0 580 45294 8 National foreword This British Standard is the official English language version of
3、 EN 12502-4:2004. The UK participation in its preparation was entrusted to Technical Committee ISE/NFE/8, Corrosion of metals and alloys, which has the responsibility to: A list of organizations represented on this committee can be obtained on request to its secretary. Cross-references The British S
4、tandards which implement international or European publications referred to in this document may be found in the BSI Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Search” facility of the BSI Electronic Catalogue or of British Standards Online.
5、This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. aid enquirers to understand the text; present to the responsible i
6、nternational/European committee any enquiries on the interpretation, or proposals for change, and keep the UK interests informed; monitor related international and European developments and promulgate them in the UK. Summary of pages This document comprises a front cover, an inside front cover, the
7、EN title page, pages 2 to 12, an inside back cover and a back cover. The BSI copyright notice displayed in this document indicates when the document was last issued. Amendments issued since publication Amd. No. Date CommentsEUROPEANSTANDARD NORMEEUROPENNE EUROPISCHENORM EN125024 December2004 ICS77.0
8、60;23.040.99;91.140.60 Englishversion ProtectionofmetallicmaterialsagainstcorrosionGuidanceon theassessmentofcorrosionlikelihoodinwaterdistributionand storagesystemsPart4:Influencingfactorsforstainlesssteels Protectiondesmatriauxmtalliquescontrelacorrosion Recommandationspourlvaluationdurisquedecorr
9、osion danslesinstallationsdedistributionetdestockagedeau Partie4:Facteursconsidrerpourlesaciersinoxydables KorrosionsschutzmetallischerWerkstoffeHinweisezur AbschtzungderKorrosionswahrscheinlichkeitin WasserverteilungsundspeichersystemenTeil4: EinflussfaktorenfrnichtrostendeSthle ThisEuropeanStandar
10、dwasapprovedbyCENon22November2004. CENmembersareboundtocomplywiththeCEN/CENELECInternalRegulationswhichstipulatetheconditionsforgivingthisEurope an Standardthestatusofanationalstandardwithoutanyalteration.Uptodatelistsandbibliographicalreferencesconcernings uchnational standardsmaybeobtainedonapplic
11、ationtotheCentralSecretariatortoanyCENmember. ThisEuropeanStandardexistsinthreeofficialversions(English,French,German).Aversioninanyotherlanguagemadebytra nslation undertheresponsibilityofaCENmemberintoitsownlanguageandnotifiedtotheCentralSecretariathasthesamestatusast heofficial versions. CENmember
12、sarethenationalstandardsbodiesofAustria,Belgium,Cyprus,CzechRepublic,Denmark,Estonia,Finland,France, Germany,Greece,Hungary,Iceland,Ireland,Italy,Latvia,Lithuania,Luxembourg,Malta,Netherlands,Norway,Poland,Portugal, Slovakia, Slovenia,Spain,Sweden,SwitzerlandandUnitedKingdom. EUROPEANCOMMITTEEFORSTA
13、NDARDIZATION COMITEUROPENDENORMALISATION EUROPISCHESKOMITEEFRNORMUNG ManagementCentre:ruedeStassart,36B1050Brussels 2004CEN Allrightsofexploitationinanyformandbyanymeansreserved worldwideforCENnationalMembers. Ref.No.EN125024:2004:EEN 12502-4:2004 (E) 2 Contents Page Foreword3 Introduction .4 1 Scop
14、e 5 2 Normative references 5 3 Terms and definitions .5 4 Materials .5 5 Types of corrosion.5 5.1 General5 5.2 Pitting corrosion 6 5.3 Crevice corrosion 8 5.4 Stress corrosion 9 5.5 Knife-line corrosion.10 5.6 Corrosion fatigue.11 6 Assessment of corrosion likelihood11 Bibliography 12 EN 12502-4:200
15、4 (E) 3 Foreword This document (EN 12502-4:2004) has been prepared by Technical Committee CEN/TC 262 “Metallic and other inorganic coatings”, the secretariat of which is held by BSI. This European Standard shall be given the status of a national standard, either by publication of an identical text o
16、r by endorsement, at the latest by June 2005, and conflicting national standards shall be withdrawn at the latest by June 2005. This standard is in five parts: Part 1: General; Part 2: Influencing factors for copper and copper alloys; Part 3: Influencing factors for hot dip galvanized ferrous materi
17、als; Part 4: Influencing factors for stainless steels; Part 5: Influencing factors for cast iron, unalloyed and low alloyed steels. Together these five parts constitute a package of inter-related European Standards with a common date of withdrawal (dow) of 2005-06. According to the CEN/CENELEC Inter
18、nal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Nether
19、lands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom. EN 12502-4:2004 (E) 4 Introduction This document mainly results from investigations into and experience gained of the corrosion of stainless steel materials used as tubes, fittings or vessels in drink
20、ing water distribution systems in buildings. However, it can be applied analogously to other supply water systems. The corrosion resistance of products made of stainless steel immersed in waters exists because of the presence of a very thin passive layer. Stainless steels in water systems are, in ge
21、neral, resistant to corrosion, although there are certain conditions under which they can sustain corrosion damage. As a result of the complex interactions between the various influencing factors, the extent of corrosion can only be expressed in terms of likelihood. This document is a guidance docum
22、ent and does not set explicit rules for the use of stainless steels in water systems. It can be used to minimize the likelihood of corrosion damages occurring by: assisting in designing, installing and operating systems from an anti-corrosion point of view; evaluating the need for additional corrosi
23、on protection methods for a new or existing system; assisting in failure analysis, when failures occur in order to prevent repeat failures occurring. However, a corrosion expert, or at least a person with technical training and experience in the corrosion field, is required to give an accurate asses
24、sment of corrosion likelihood or failure analysis. NOTE Stainless steels are used for domestic pipework, in the food industry and, more importantly, in the chemical industry covering a variety of aggressive environments and service conditions. This explains the existence of a significant number of s
25、teel grades each with specific corrosion resistance and also specific mechanical properties. EN 12502-4:2004 (E) 5 1 Scope This document gives a review of influencing factors of the corrosion likelihood of stainless steels used as tubes, tanks and equipment in water distribution and storage systems
26、as defined in EN 12502-1. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
27、EN ISO 8044:1999, Corrosion of metals and alloys Basic terms and definitions (ISO 8044:1999). EN 12502-1:2004, Protection of metallic materials against corrosion Guidance on the assessment of corrosion likelihood in water distribution and storage systems Part 1: General. 3 Terms and definitions For
28、the purposes of this document, the terms and definitions given in EN ISO 8044:1999 and EN 12502- 1:2004 apply. 4 Materials For the purpose of this document, the term “stainless steel” includes all martensitic, ferritic, austenitic-ferritic and austenitic steels conforming to the requirements of EN 1
29、0088-1 2, EN 10088-2 3 and EN 10088-3 4. Examples of steel grades that are used or that can be considered as candidate materials for supply water installations are listed in EN 10312 5. This document also applies to stainless casting alloys, which are commonly used for the production of valves and f
30、ittings and which are of the same composition type as the steels listed in EN 10088, Parts 1 to 3. The casting alloys can be considered as equivalent to their wrought counter parts, provided that no sensitization of the material remains after manufacturing (to be checked by testing the resistance ag
31、ainst intergranular corrosion). 5 Types of corrosion 5.1 General The most common types of corrosion are described in EN 12502-1:2004, Clause 4. The rate of uniform corrosion of stainless steels in water distribution and storage systems is negligible because of their passive state. Under the conditio
32、ns prevailing in water systems stainless steels are usually the more noble materials and hence are not endangered by bimetallic corrosion. The likelihood of intergranular corrosion is negligible in the systems under consideration. Discoloration of the materials surface resulting from deposition of f
33、oreign corrosion products is not indicative of corrosion of the stainless steel. EN 12502-4:2004 (E) 6 In some cases, however, the passive layer of these materials can be locally destroyed. This can result in localized corrosion attack, which can lead to failure because of corrosion damage. The type
34、s of corrosion considered for stainless steels comprise the following: pitting corrosion; crevice corrosion; stress corrosion; knife-line corrosion; corrosion fatigue. For each type of corrosion, the following influencing factors (described in EN 12502-1:2004, Table 1 and Clause 5) are considered: c
35、haracteristics of the metallic material; characteristics of the water; design and construction; pressure testing and commissioning; operating conditions. 5.2 Pitting corrosion 5.2.1 General Pitting corrosion occurs only when the potential is more noble than a critical value, which is referred to as
36、pitting initiation potential. The pitting initiation potential depends on parameters related to both the material and the water composition. Pitting corrosion can occur only if the redox-potential of the water is more positive than the pitting initiation potential. 5.2.2 Influence of the characteris
37、tics of the metallic material The likelihood of pitting corrosion in stainless steels decreases with increasing chromium, molybdenum and nitrogen contents. It is increased for sulfur-enriched stainless steels (e.g. free-cutting stainless steels used for valves and fittings). Clean metal surfaces exh
38、ibit the smallest likelihood of pitting corrosion. Mechanical damage to the surface of finished products, e.g. by scratching or coarse grinding, results in an increased susceptibility of stainless steels to pitting corrosion and stress corrosion cracking. Metallic particles of unalloyed and low-allo
39、y steels can become embedded in the stainless steel surface during machining or handling. They can act as small anodes of corrosion cells, the cathode of which is the stainless steel. In the course of the dissolution of the anodes, the local concentration of chloride ions will be increased by ion mi
40、gration, and therefore the likelihood of pitting corrosion increases. Furthermore, the corrosion likelihood can also be increased by the iron (III)-bearing corrosion products formed during the dissolution of the anodes, because these corrosion products are more effective oxidizing agents than the di
41、ssolved oxygen and favour the conditions necessary for the occurrence of pitting corrosion. Sensitization can also lead to an increase in the likelihood of pitting corrosion. Incorrect heat treatment or welding procedures, where the material remains for a prolonged period of time in the temperature
42、range of EN 12502-4:2004 (E) 7 500 C to 800 C leads to precipitation of chromium-rich carbides at the grain boundaries and consequent depletion of chromium in the vicinity of the boundaries. This change in the material is referred to as sensitization. Sensitization can be revealed by testing in acco
43、rdance with EN ISO 3651-2 6. Materials in the as-fabricated condition should be resistant to this test. Sensitization during fabrication and welding, especially with wall thicknesses greater than 6 mm, can be avoided by following the recommendations from the materials manufacturer. 5.2.3 Influence o
44、f the characteristics of the water The likelihood of pitting corrosion of stainless steels increases as the chloride ion concentration in the water increases, if the other service conditions remain constant. The likelihood of pitting corrosion (within the limits of supply water) is either decreased
45、or the pitting corrosion is not influenced by the presence of other anions. The likelihood for pitting corrosion of non-molybdenum-bearing ferritic and austenitic stainless steels in cold water becomes high when the chloride ion concentration exceeds about 6 mmol/l. For hot water the limiting chlori
46、de ion concentration for these alloys is lower, possibly less than 1,5 mmol/l depending on other factors discussed in 5.1 to 5.6. 5.2.4 Influence of design and construction The likelihood of pitting corrosion and crevice corrosion is increased by welding defects such as filler metal sagging, incompl
47、ete root pass, edge misalignment, open pores, weld metal splashing, slag residuals on both base and weld materials. During the welding process, oxide films and scales can be formed that highly increase the likelihood of pitting corrosion. This can be avoided by gas-shielded welding methods, where at
48、tention is paid to proper supply and guidance of shielding and purging gas. Oxide films that exhibit colours darker than that of straw strongly increase the likelihood of pitting corrosion. Removal of oxide films can be achieved by pickling (with pickling agents free from hydrochloric acid), fine grinding or shot peening, e.g. with glass beads. Under critical conditions (e.g. depending on material and water composition and temperature) even straw-coloured oxide films increase the
